Way Beyond Monochrome 2nd ed. - some clarification needed please

swmcl · Jul 22, 2015

Just trying to get my head around things ...

I refer you to Figure 7 of the chapter titled, 'Customising Film Speed and Development' (pp.221 in my book)

My query relates to the feature which is noted 'exposure = 0.80'.

This is the amount of exposure that was required to produce 0.17 density above f+b I believe.

0.80 is 2.666 (2 2/3) times 0.3 which means 2 and 2/3rds stops does it not ? So it would mean the film was rated at say box speed of say 250 for the test and the test reveals a truer speed in the region of 40 or so ?

Am I correct ?

This would mean the reference of 0 on the graph correlates to a point 4 stops lower than 'Zone 5' ... correct ?

Two separate questions from the same graph.

Cheers in advance.

Steve

Alan9940 · Jul 22, 2015

Hi Steve,

I don't have or have ever seen the book you reference, but...

0.17 above f+b is defining the exposure threshold of the film tested. That is, the minimum amount of exposure required to have any measurable density on the film. IMO it's a little high; I usually shoot for about 0.10 above f+b.

No clue what the 0.80 number means. Without the "exposure =" part of it I'd look at that number and think CI (contrast index) which is a parameter of development. Again, a little high if you're printing on graded silver gelatin papers; maybe close for variable contrast silver gelatin papers; and a little low for alternate processes such as platinum/palladium, gum, etc. Many folks develop their film to a certain CI, but I have always developed for a printable Zone VIII density. Btw, I'm talking about B&W film here.

I hope something I've said helps.

Best regards,
AlanH

Nathan King · Jul 22, 2015

I'll take a look at my book when I get home, if the co-author of the book doesn't respond first, which he probably will.

Stephen Benskin · Jul 22, 2015

0.80 is relative log exposure. In this type of example it relates to the differences in the step tablet densities. Let's say the step tablet is in 1/2 stop intervals (0.15), 0.80 is 5 1/3 steps from the densest step. Most step tablets have a 10 stop (3.0 log) range. Notice the last density point for the "Normal" curve has a relative log exposure of 3.0.

swmcl · Jul 23, 2015

Thanks all for your replies.

I'm not sure things are that much clearer for me. (It's me not you I'm sure ...!)

Silveror0 I am trying to relate it to the AA book too. It sure can be a head-spin !

swmcl · Jul 23, 2015

I've got an understanding that Mr Lambrecht is measuring the speed point at Zone 1.5. I believe Mr Lambrecht is also saying the correct speed for the film has been chosen when the density at Zone 1.5 is 0.17 above f+b. As I understand it, the Ansel Adams way is to measure the speed at Zone 1 and with a density of 0.1 above f+b.

Effectively, Mr Lambrecht is measuring the speed point a little higher on the curve.

For what its worth I think Mr Lambrecht is probably on the money with his methods for practical people.

I'm still no clearer on the 0.80 thing though ...

RalphLambrecht · Jul 23, 2015

Steve,I caught this on my laptop;later todayI'll get to my desktop ,can look at the book at the same time and will answer again

RalphLambrecht · Jul 23, 2015

Alan9940 said:
Hi Steve,

I don't have or have ever seen the book you reference, but...

0.17 above f+b is defining the exposure threshold of the film tested. That is, the minimum amount of exposure required to have any measurable density on the film. IMO it's a little high; I usually shoot for about 0.10 above f+b.

No clue what the 0.80 number means. Without the "exposure =" part of it I'd look at that number and think CI (contrast index) which is a parameter of development. Again, a little high if you're printing on graded silver gelatin papers; maybe close for variable contrast silver gelatin papers; and a little low for alternate processes such as platinum/palladium, gum, etc. Many folks develop their film to a certain CI, but I have always developed for a printable Zone VIII density. Btw, I'm talking about B&W film here.

I hope something I've said helps.

Best regards,
AlanH

Alan is close,I try to make negatives with a tonal range from ZoneI.5 to Zone VII.5 and my target densities for those are 0.17and 1,37, respectively for atotal density range of1.2,which is roughly a grade 2 paper.I think the 0.8 value refers to negative contrast but again ,I'll check later to be sure

swmcl · Jul 23, 2015

Thanks Ralph. Looking forward to further discussions.

Stephen Benskin · Jul 24, 2015

The 0.80 relative exposure is part of how to determine the film's EI. The relative exposures at the 0.17 speed point from the different development times are plotted on a gradient/relative exposure graph (figures 12a - 12c). EIs for different gradients can then be calculated from the graph.

Way Beyond Monochrome 2nd ed. - some clarification needed please

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